In the field of value printing, as for example in postage meter machines, a constant vigil is maintained to assure that the taking of fraudulent impressions from the value printing die surface of a printing member is prevented. In a reciprocating platen type of postage meter machine, this is of a particular concern since the print head of such machines is not rotated out of exposure as occurs with a rotatary type postage meter machine. One scheme for preventing the taking of fraudulent impressions is disclosed in U.S. Pat. No. 2,350,853 wherein a manually operable postage meter machine of the reciprocating type is disclosed. A rocker member with a plunger portion is utilized to prevent fraudulent impression taking. The plunger portion extends within a printing die block and is normally located beyond the perimeter of the printing dies. Although such a device functions quite well in a mechanical postage meter machine, it obviously would be impractical to adapt it for present day postage meter machines, because of the compactness and generally automatic functioning of the latter. The problem with preventing fraudulent impression taking involves exposure of the print head. The print head may be "wiped" when exposed i.e., an envelope or tape may be pressed against the print head to obtain unauthorized postage. In considering schemes for preventing such fraudulent taking of postage, problems arise with postage meter mailing machines because the print head must be exposed during a period of operation and a wrongdoer may stop operation at this particular period and obtain fraudulent impressions if no safeguards are taken.